Surface conversion treatment for magnesium alloys

ABSTRACT

An aqueous composition for surface conversion treatment of magnesium and magnesium alloys prior to application of a painted or photoresist coating is described. The composition comprises a water solution of about 9.4 to about 19.5 grams per liter NH4 ; about 50 to about 103 grams per liter PO4 ; about 1.0 to about 2.8 grams per liter Ca ; and a total of about 1.9 to about 4.8 grams per liter of ions selected from the group consisting of Cl , NO3 , and SO4 , and is characterized by having a pH of about 3.0 to about 4.5.

United States Patent Brown Jan. 8, 1974 [541 SURFACE CONVERSION TREATMENT FOR 1,709,894 4/1929 Burdick 148/615 R MAGNESIUM ALLOYS 3,218,200 11/1965 Henricks 148/615 Z 3,178,320 4/1965 Henricks 148/615 Z {75] Inventor: James A. Brown, M1d1and, Mich. 3,409 525 1 1953 Z [73] Assignee, The Dow Chemica' Company 3,090,709 5/1963 Henncks 143/ 15 H h Midland, Mich.

Primary Examiner-Ralph S. Kendall [221 Med: Oct. 26, 1971 Appl. No.1 192,558

Related US. Application Data Continuation-impart of Ser. No. 89,130, Nov. 12, 1970, abandoned.

References Cited UNITED STATES PATENTS 1/1962 Jayne 148/615 R 11/1966 Harwell et 148/6115 Z 9/1963 Goldsmith 148/615 Z Assistant Examiner-M. G. Wityshyn At't0rneyWilliam M. Yates et a].

57 ABSTRACT An aqueous composition for surface conversion treatment of magnesium and magnesium alloys prior to application of a painted or photoresist coating is described. The composition comprises a water solution of about 9.4 to about 19.5 grams per liter NHJ; about to some grams per menace; aqua-2,19 about 2.8 grams per liter Ca and a total of about 1.9

59 Claims, No Drawings 1 SURFACE CONVERSION TREATMENT FOR" MAGNESIUM ALLOYS A methodis also described for producing the composition by mixing with water about 60 to about 125 grams per liter of final composition of monobasic am monium phosphate; sufficient calcium salt of 'a strong surface promotes adherence of a photoresist material and/or paint to the magnesium surface.

BACKGROUND OF THE INVENTION The present application is a continuation-in-part of a copendihg application, Ser. No. 89,130, filedNov. l2, l970 by James A. Brown now abandoned.

This invention relates to an acidic composition and a method for employing said composition for the surface treatment of metals. More particularly, the invention pertains toan aqueous acidic composition and a method of usingsaid composition for thesurface conversionl treatment of magnesium and/or magnesium basealloys. Hereinafter, magnesium-andalloys of mag nesium containing in excess of 50 percent magnesium are referred toas magnesium.

To achieve an adherent bond'between magnesium andan overcoating, such as paint or a photoresist material, it is necessary to treat the-metal surface prior to application of the overcoating; Although treatments are available for preparing-ametal for application of an overcoating, a new surface conversion treatment was needed for magnesium photoengraving sheet, which would promote effective adhesion between the magnesium and: the photoresist material.

Photoresist materialsare those which are suitable for coating on metal and have a minimum shelf-life, i.e., storage time, of approximately 6 months. Polyvinyl cinnamate type photoresists are an exampleof such overcoatings. Photoresist materials, especially those utilized in. powderless etching baths, inherently have poor adhesion and etch resistance, when applied to bare magnesium surfaces.

To be satisfactorily employed as a pretreament prior to application of a photoresist, a surface conversion composition should possess certain characteristics. Foremost among these are that the conversion solution should be such that it can be readily and rapidly applied to aclean magnesium surface to produce a light colored coati'ng, which promotes adhesion between the magnesium surface and the overcoating of photoresist. The conversion layer should possess the characteristic of providing sufficient adherence of the photoresist to permit a detergent scrubbing and re-etching with dilute nitric acid without failure of the resist film after removal of the plate from a powderless etching bath. Moreover, the conversion layer formed on the magnesium surface must be compatiblepwith the photoresist sothat no detrimental reaction will occur between said layer and the photoresist to substantially effect the shelf-life of a coated product.

The treatment should also enhance the adhesion characteristics between the magnesium surface and paint applied 'thereto.

It is, therefore, an object of this invention to provide a composition capable of conditioning a magnesium surface for application of an overcoating of paint or photoresist materials. I

It is another object of this invention to provide a method of preparing a surface conversion composition capable of improving the adherence between magnesium metals and photoresist and paint coatings.

It is yet another object of this invention to provide a process of using an improved composition to coat magnesium. or magnesium alloy surfaces precedent to adhering paint orphotoresist materials to the magnesium surfaces.

Other objects and advantages will become apparent during the course of the following description of the invention.

SUMMARY OF THE lNVENTlON The above objects and advantages have been achieved in an aqueous composition comprising a water solution of about 9.4 to about 19.5 grams per liter NH, and about 50 to about 103 grams per liter POf. The composition further includes about 1.0 to about 2.8 gramsper liter Ca and. a total of about 1.9 to about 4.8 grams per liter of ions selected from the groupconsisting of CI, N0 and S0 The composition is characterized by a pH of about 3.0 to about 4.5. Throughout the specification and appended claims alljproportions are specified relative to a liter of finished or completed composition, unless otherwise indicated.

The aforementioned acidic aqueous composition is applied as a liquid. to the clean surface of magnesium alloys at a temperature of up to about F. As used herein the term clean meanssubstantially free of oxide and oily materials. Upon contacting a-clean magnesium surface with the composition, a reaction occurs uniformly over the magnesium surface. The reacting is evidenced by a visually continuous lighter colored metallic or white surface coating on the magnesium. To realize the benefits of this treatment, the magnesium alloy surface should be rinsed in liquid water at a temperature of up to about 130F. The rinse water can either be ordinary tap water or distilled water without materially altering the effectiveness of this invention.

In a preferred embodiment, the aqueous composition comprises about60 to about, grams per liter of monobasic ammonium phosphate; sufficient calcium salt of a strong acid to produce a Ca concentration of about 1.0 to about 2.8 grams per liter; and sufficient pH modifier selected as required from the group consisting of phosphoric acid and ammonium hydroxide to produce a pH of about 3.0 to about 4.5. Various calcium salts of strong mineral acids are included in this composition. Among the suitable calcium salts are calcium chloride, calcium nitrate, and calcium sulfate. The hydrated derivatives of the aforementioned compounds are also suitable, for example, approximately 4 to about 10 grams per liter of CaCl -2l-l O supplies sufficient Ca and Clto produce a satisfactory treating composition. Moreover, anhydrous calcium chloride and other hydrated forms thereof, such as the monohydrate, dihydrate, or hexahydrate are also acceptable when they are employed in amounts sufficient to provide the required amount of Ca ion.

Sufficient calcium ion can be attained in said composition by addition of a single calcium salt of a strong mineral acid such as, for example, calcium chloride, calcium nitrate and calcium sulfate. Moreover, any combination of these calcium bearing compounds in an amount sufficient to provide Ca ion within the stipulated range can be used.

It has been ascertained that a further improvement in performance will be realized when the previously de scribed aqueous composition comprises about 80 to about 105 grams per liter of monobasic ammonium phosphate and an amount of Ca ion as furnished by about 6 to about 8 grams per liter of dihydrated calcium chloride or equivalent quantities of anhydrous or hydrated calcium nitrate, or calcium sulfate. This amount of dihydrated calcium chloride provides Ca within the range of about 1.8 to about 2.4 grams per liter of solution. The pH will enhance the effectiveness of the solution when it is within the range of about 3.4 to about 3.7. Within this pH range, reaction of the composition with the magnesium surface will be optimized. An excessively low pH results in insufficient surface coating and inferior adhesion of the photoresist material to the magnesium surface. An excessively high pH, however, results in a heavy powdery surface, which will absorb dye from the photoresist causing poor contrast and an undesirably rough photoresist coating.

Aluminum, magnesium, zinc, and various chromates may be present, along with other impurities normally associated with commercial sources of ingredients used in the composition without hindering the effective utilization of said solution.

The composition of this embodiment can be further characterized as being ionically neutral. That is, the specific combination of compounds forming this solution results in the occurrence of equivalent ionic charges in the final conversion composition.

Various methods of forming said composition can be visualized, but it is preferred that the composition be produced by a process comprising mixing together water with about 60 to about 125 grams per liter of final composition of monobasic ammonium phosphate; sufficient calcium salts of a strong mineral acid to produce a Ca concentration of about 1.0 to about 2.8 grams per liter of final composition; and sufficient pH modifier to adjust the pH of the final composition to about 3.0 to about 4.5 wherein said pH modifier is selected as required from the group consisting of phosphoric acid and ammonium hydroxide.

The mode of mixing the composition is unimportant and can be accomplished by a number of methods. Mixing by stirring, passing of air through the solution, vibrating the container for said composition or agitation with an impeller are among the satisfactory means of mixing the composition.

Varying amounts of precipitate will usually form during the aforementioned mixing. To reduce the concentration of precipitate, which is believed to be primarily composed of calcium phosphate, a step of removing the precipitate from the final composition can be incorporated after the mixing or agitation has been concluded. While the precipitate can be easily removed by means of a centrifuge it is preferred the precipitate be removed by filtering the composition through a medium having pores no greater than about 50 microns in diameter. Use of the filtered composition for treating metal lic surfaces prior to painting or coating with a photoresist will result in a smooth surface free of calcium phosphate precipitate.

Though the above mixing process is completely operable, it is oftentimes desirable to have a composition containing a minimum of precipitate prior to filtering.

This can be of economic benefit when substantial quantities of the conversion liquid are being formed. The precipitation of calcium phosphate can be minimized by sequentially mixing the aforementioned constituents in the recited order together in water. A further reduction in precipitate can be effected by dissolving the calcium compound in water prior to mixing with the remaining constituents in the composition. Adjusting the volume and concentration of the solution may be accomplished at any step by a further addition of water.

In the practice of treating magnesium surfaces according to the invention, a clean magnesium surface is contacted with a describedaqueous composition at a liquid temperature of up to about 120F. for a sufficient time to permit a lighter colored metallic or white coating to form on the surface. After removing the magnesium from the aqueous bath, the reacted surface is rinsed with liquid water at a temperature of up to about 130F. Temperatures exceeding those stated above should be avoided, since the phosphate coating begins to significantly redissolve in water at higher temperatures. Any means of cleaning the metal surface prior to reacting with said composition is satisfactory. Exemplarily of such cleaning methods are contacting the surface with rotating abrasive brushes, alkaline solutions, a pumice slurry, and the like. Rinsing of the sheet after cleaning can be adequately accomplished in water.

The precise method used for treating the magnesium with the composition is not critical so long as the composition uniformly contacts the metal surface. Methods such as spraying, dipping, brushing, or swabbing are among those completely satisfactory methods foreseeable to those skilled in the art.

Prior to applying a photoresist material to the treated metal surface to form photoengraving plate, or applying paint to the treated metallic surface, it is preferable that drying of the rinsed surface be accomplished. The treated and rinsed surface can be adequately dried by exposure to air or a heating means such as electrical coils or a plurality of heat lamps.

A uniform phosphate coating can be applied to a magnesium surface, such as sheet or plate, within about 1 minute at reaction temperaturesup to about 120F. when contacting is carried out by immersion or spraying the solution onto the magnesium surface. Reacting times as short as about 15 seconds up to about 45 seconds have proven to be adequate and are preferred. In general, it is desired that reacting be accomplished at a low temperature and it is, therefore, desirable that temperatures of about F. to about F. be maintained during the reacting period.

EXAMPLE l A surface conversion composition was prepared in a 55 gallon polyethylene lined drum using the following sequence of steps:

a. filling the 55 gallon drum three-fourth full with water,

5. b. adding 50 milliliters of phosphoric acid (H' PO f. holding thesolution of step e overnight to permit any precipitate that may have formed to settle, gQfiltering the solution into a clean' drum through a 25 micron filter. The pH of the final composition was tested and deter minedto be 3.89.

Treatment of a magnesiumalloy sheet with this composition produced a visually uniform surface coating.

EXAMPLE 2 A second surface conversion composition was prepared in a 157 gallon tank by sequentially carrying out the following steps:

a. adding 125 gallons of water to the tank and starting a circulating pump for agitation,

bL adding 250 milliliters of phosphoric acid to the tank containing water,

c. dissolving 115 pounds of monobasic ammonium phosphate in the solution of step b,

(1. adding 1 ounces of dihydrated calcium chloride, which had been previously dissolved in 4 gallons of water, to the solution of step c,

e. adding sufficient water to form 157 gallons of solution,

f. while agitation was continued, the solution was filtered through a 25 micron filter bed for 1 hour and recycled into the tank.

The finalcomposition was determined to have a pH EXAMPLE 3 A surface conversion composition with a pl-lof 3.56

was prepared in 225 gallon capacity tank as follows:

a. adding about 150 gallons of water and then 800 milliliters of phosphoric acid to the tank,

b. dissolving, with agitation, 200 pounds of monobasic ammonium phosphate in the solution of step c. dissolving16.5 pounds of technical grade dihydrated calcium chloride in 12 gallons of water and then adding thecalcium chloride solution tothe step b solutionwhile strongly agitating the solution,

d. niixing sufficient water with the step c solution to form 225 gallons of solution and then filtering this solution through a 25 micron media.

A satisfactory surface coating was obtainedon the hereinafter described PE alloy magnesium sheet treated with a conversion solution prepared as above.

EXAMPLE 4 A surface conversion solution with a pH of about 3.0 is prepared as described in Example 3 except that approximately 1,500 milliliters of phosphoric acid is added to the solution to increase the acidity. PE alloy magnesium sheet treated with this solution will have a surface witha useable coating.

EXAMPLE 5' An 18 inches by 24 inches by 0.064 inch magnesium alloy sheet was treated with the composition of Example 2. The magnesium base alloy sheet had an alloy designation of PE and had a nominal chemical composition of 3.2 percent aluminum and 1.1 percent zinc.

The magnesium sheet was first cleaned by contacting the sheet with rotating abrasive lbrushes, which had been coated with 320 grit silicon carbide particles. The sheet was flushed with water during the cleaning step. Following cleaning with the abrasive brushes the magnesium sheet againwas water rinsed.

Treatment with the composition of Example 2 consisted of immersing the PE alloy sheet into the conversion composition for a period of 20 seconds. During the immersion step, the composition was maintained at a temperature of F. to F. and continuously agitated by pumping through a recirculatory type system. The return composition was directed toward the immersed magnesium sheet through ports in two pipes beneath the bath surface.

Upon removal of the magnesium sheet from the composition, the sheet was rinsed by spraying with water which wasmaintained at a temperature of 65F. to 75F. and then dried by heating to a temperature of 250F. in an infrared drying oven. After drying the surface, a polyvinyl cinnamate type photoresist was applied to the surface to form photoengraving sheet.

Upon furtherprocessing, it was ascertained that the phosphate coating promoted sufficient adhesion between the magnesium sheet and photoresist material to permit the photoresist overcoating to resist acid attack in the image areas of the photoengraving sheet. Fur thermore, the adhesion characteristicswere sufficient to allow scrubbing with a detergent and re-etching with dilute nitric acid after the processed photoengraving sheet was removedfrom a powderless etching bath without failure or a loss of the resist film from image areas. The photoengraving sheet so produced had a shelf-life of a minimum of 6 months.

EXAMPLE 6 Magnesium alloy PE sheet was processed in a manner similar to that of Example 5 and painted with one coat of Dulux Black Enamel 83-005 after the magnesium surface had dried. The painted surface was tested for adherence of the paint to the sheet, corrosion protection in a 5 percent salt spray, and blistering at F. in an atmosphere having a relative humidity of 95 percent. The tests indicated the phosphate conversion coating provided an adequate base for painting the metal surface.

What is claimed is:

1; An aqueous magnesium surface treating composition comprising: 1

awater solution of about 9.4 to about 19.5 grams per liter Nl-lf; i about 50 to about 103 grams per liter POf; about 1.0 to about 2.8 grams per liter Ca;

and a total of about 1.9 to about 4.8 grams per liter of ions selected from the group consisting of Cl, N03", and SO4 said composition being characterized by a pH of about 3.0 to about 4.5.

2. The aqueous composition of claim 1 wherein the pH is about 3.4 to about 3.7.

3. The composition of claim l including from about 1.8 to about 2.4 grams per liter Ca.

4. A process comprising:

a. contacting a clean magnesium surface with a liquid aqueous composition of claim 1 at a temperature of up to about 120F.; and

b. rinsing the contacted surface 'in liquid water at a temperature of up to about 130F.

5. The process of claim 4 wherein the magnesium surface is contacted with the aqueous composition for a time of up to about one minute.

6. The process of claim 4 wherein the magnesium surface is contacted with the aqueous composition for a time of from about 15 to about 45 seconds.

7. The process of claim 4 including the additional step of removing precipitate from the composition prior to step (a).

8. The process of claim 4 wherein a phosphate containing layer is formed on the magnesium surface contacted with the composition, the phosphate containing layer promoting effective adhesion of a photoresist material to the magnesium surface.

9. The process of claim 4 including as step (c) drying the rinsed surface.

10. The process of claim 9 including as step ((1) applying paint to the dried surface.

11. The process of claim 9 including as step (d) applying a photoresist material to the dried surface.

12. The process of claim 11 wherein the magnesium surface is of an alloy having a designation of PE.

13. The process of claim 11 wherein a polyvinyl cinnamate type photoresist is applied to the dried surface.

14. The process of claim 11 wherein the treated and dried surface having photoresist applied thereon has a shelf-life of at least about six months.

15. The process of claim 4 wherein contacting is carried out with the aqueous composition after filtering the composition through a medium with pores no greater than about 50 microns in diameter.

16. The process of claim 15 wherein the pores are no greater than 25 microns in diameter.

17. The process of claim 4 wherein contacting is carried out at a temperature of about 70F. to about 90F.

18. The process of claim 17 wherein the magnesium surface is contacted with the aqueous composition for a time of up to about 1 minute.

19. An aqueous magnesium surface treating composition consisting essentially of a water solution of about 9.4 to about 19.5 grams per liter Nl-lf';

about 50 to about 103 grams per liter POI";

about 1.0 to about 2.8 grams per liter Ca;

and a total of about 1.9 to about 4.8 grams per liter of ions selected from the group consisting of Cl, N and S0 said composition characterized by a pH of about 3.0

to about 4.5 and being free of particulate removable by filtering through a medium with pores no greater than about 50 microns in diameter.

20. A process comprising:

a. contacting a clean magnesium surface with a liquid aqueous composition consisting essentially of a water solution of about 9.4 to about 19.5 grams per liter NHI, about 50 to about 103 grams per liter POI, about 1.0 to about 2.8 grams per liter Ca, and a total of about 1.9 to about 4.8 grams per liter of ions selected from the group consisting of Cl, N0 and S0 said composition being characterized by a pH of about 3.0 to about 4.5 at a temperature of up to about 120F.;

b. rinsing the contacted surface in liquid water at a temperature of up to about 130F.;

c. drying the rinsed surface; and

d. applying a photoresist material to the dried surface.

21. An aqueous magnesium surface treating compositon comprising:

about 60 to about 125 grams per liter of monobasic ammonium phosphate;

sufficient calcium salt of a strong mineral acid to produce a Ca concentration of about 1.0 to about 2.8 grams per liter; and

sufficient pH modifier elected as required from the group consisting of phosphoric acid and ammonium hydroxide to produce. a pH of about 3.0 to about 4.5.

22. The aqueous composition of claim 21 including sufficient pH modifier to produce a pH of about 3.4 to about 3.7.

23. The aqueous composition of claim 21 wherein the calcium salt is calcium chloride.

24. The aqueous compositionof claim 21 wherein the calcium salt is calcium nitrate.

25. The aqueous composition of claim 21 wherein the calcium salt is calcium sulfate.

26. The aqueous composition of claim 21 comprising about to about grams per liter monobasic ammonium phosphate; and

sufficient calcium salt to produce a Ca concentration of about 1.8 to about 2.4 grams per liter.

27. The aqueous solution of claim 26 including sufficient pH modifier to produce a pH of about 3.4 to about 3.7.

28. A process comprising:

a. contacting a clean magnesium surface with a liquid aqueous composition of claim 27 at a temperature of up to about F., and

b. rinsing the contacted surface in liquid water at a temperature of up to about F.

29. The process of claim 28 including the additional step of removing precipitate from the composition prior to step (a).

30. The process of claim 28 including as step (c) drying the rinsed surface.

31. The process of claim 30 including as step (d) applying a photoresist material to the dried surface.

32. The process of claim 30 including as step (d) applying paint to the dried surface.

33. The process of claim 30 wherein contacting is carried out with the aqueous composition after filtering the composition through a medium with pores no greater than about 50 microns in diameter.

34. The process of claim 33 wherein the pores are no greater than 25 microns in diameter.

35. The process of claim 30 wherein contacting is carried out at a temperature of about 70F. to about 90F. I

36. The process of claim 32 wherein the magnesium surface is contacted with the aqueous composition for a time of up to about one minute.

37. A process comprising mixing together:

a. water;

b. about 60 to about 125 grams per liter of final composition of monobasic ammonium phosphate;

c. sufficient calcium salt of a strong mineral acid to produce a Ca concentration of about 1.0 to about 2.8 grams per liter of final composition; and

d. sufiicient pH modifier to adjust the pH of the final composition to about 3.0 to about 4.5 wherein the pH modifier is selected as required from the group consisting of phosphoric acid and ammonium hydroxide.

38. The process of claim 37 wherein step (b) comprises mixing about 80 to about 105 grams per liter of final composition of monobasic ammonium phosphate; and step (c) comprises mixing sufficient calcium salt to produce a Ca" of about 1.8 to about 2.4 grams per liter 'of final composition.

39. The process of claim 37 wherein step (c) comprises mixing an aqueous solution of the calcium salt.

40. The process of claim 37 wherein step (d) comprises adding sufficient pH modifier to adjust the pH to about 3.4 to about 3.7.

41. The process of claim 37 wherein the calcium salt is calcium chloride. 7

42. The process of claim 37 wherein the calcium salt is calcium nitrate.

43. The process of claim 37 wherein the calcium salt is calcium sulfate.

44. The process of claim 37 including removing precipitate from the final composition.

45. The process of claim 44 wherein removing cal cium phosphate precipitate is carried out by filtering through a medium with pores no greater than about 50 microns in diameter.

46. The process of claim 37 comprising sequentially mixing together in water diluted phosphoric acid the constituents of steps (b), (c), and (d).

47. The process of claim 46 including removing precipitate from the final composition.

48. A process comprising:

a. mixing phosphoric acid with position;

b. mixing about 60 to about 125 grams per liter of final composition of monobasic ammonium phosphate into the composition of step (a);

c. mixing into the composition of step (b) sufficient calcium salt of a strong mineral acid in aqueous solution to produce a final Ca concentration of about 1.8 to about 2.4 grams per liter of final composition;

water to form a comd. adding sufficient pl-l modifier to the composition of step (c) to adjust the pH to about 3.4 to about 3.7 wherein the pH modifier is selected from the group consisting of phosphoric acid and ammonium hydroxide;

e. adding sufficient water to the composition of steps (a), (b), (c), and (d), to attain the desired volume;

f. filtering the composition of step (d) through a medium with pores no greater than about 50 microns in diameter;

g. contacting a clean magnesium surface with the composition of step (f) at a temperature of about F. to about F. for up to about 1 minute;

h. rinsing the contacted surface in liquid water at a temperature of up to about F.;

i. drying the rinsed surface; and

j. applying a photoresist material to the dried surface to form photoengraving sheet.

49. The process of claim 48 wherein the calcium salt is calcium chloride.

50. The process of claim 48 wherein the calcium salt is calcium nitrate.

51. The process of claim 48 wherein the calcium salt is calcium sulfate.

52. The process of claim 48 wherein the magnesium surface is of an alloy having a designation of PE.

53. The process of claim 48 wherein a polyvinyl cinnamate type photoresist is applied to the dried surface.

54. The process of claim 48 wherein the magnesium surface is contacted with the aqueous composition for a time of from about 15 to about 45 seconds.

55. The process of claim 48 wherein the pores are no greater than 25 microns in diameter.

56. The process of claim 48 wherein the magnesium surface in step (g) is immersed in 'the composition of step (f).

57. The process of claim 48 wherein the magnesium surface in step (g) is sprayed with the composition of step (f).

58. The process of claim 48 wherein the treated and dried surface having photoresist applied thereon has shelf-life of at least about 6 months.

59. The process of claim 48 wherein a phosphate containing layer is formed on the magnesium surface contacted with the composition, the photoresist containing layer promoting effective adhesion of a photoresist material to the magnesium surface.

jgggg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION January 8, 1974 Patent No. 3, 7 4, 4:17 Dated v fl James A; Brown I It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 8, line 17, change "elected" to -selected-.

Signed and, sealed this 17thday of September I974.

(SEAL) Atcestz McCOY ;M. GIBSON JR. 0. MARSHALL DANN f Attesting Officer Commissioner of Patents 

2. The aqueous composition of claim 1 wherein the pH is about 3.4 to about 3.7.
 3. The composition of claim 1 including from about 1.8 to about 2.4 grams per liter Ca .
 4. A process comprising: a. contacting a clean magnesium surface with a liquid aqueous composition of claim 1 at a temperature of up to about 120*F.; and b. rinsing the contacted surface in liquid water at a temperature of up to about 130*F.
 5. The process of claim 4 wherein the magnesium surface is contacted with the aqueous composition for a time of up to about one minute.
 6. The process of claim 4 wherein the magnesium surface is contacted with the aqueous composition for a time of from about 15 to about 45 seconds.
 7. The process of claim 4 including the additional step of removing precipitate from the composition prior to step (a).
 8. The process of claim 4 wherein a phosphate containing layer is formed on the magnesium surface contacted with the composition, the phosphate containing layer promoting effective adhesion of a photoresist material to the magnesium surface.
 9. The process of claim 4 including as step (c) drying the rinsed surface.
 10. The process of claim 9 including as step (d) applying paint to the dried surface.
 11. The process of claim 9 including as step (d) applying a photoresist material to the dried surface.
 12. The process of claim 11 wherein the magnesium surface is of an alloy having a designation of PE.
 13. The process of claim 11 wherein a polyvinyl cinnamate type photoresist is applied to the dried surface.
 14. The process of claim 11 wherein the treated and dried surface having photoresist applied thereon has a shelf-life of at least about six months.
 15. The process of claim 4 wherein contacting is carried out with the aqueous composition after filtering the composition through a medium with pores no greater than about 50 microns in diameter.
 16. The process of claim 15 wherein the pores are no greater than 25 microns in diameter.
 17. The process of claim 4 wherein contacting is carried out at a temperature of about 70*F. to about 90*F.
 18. The process of claim 17 wherein the magnesium surface is contacted with the aqueous composition for a time of up to about 1 minute.
 19. An aqueous magnesium surface treating composition consisting essentially of a water solution of about 9.4 to about 19.5 grams per liter NH4 ; about 50 to about 103 grams per liter PO4 ; about 1.0 to about 2.8 grams per liter Ca ; and a total of about 1.9 to about 4.8 grams per liter of ions selected from the group consisting of Cl , NO3 , and SO4 ; said composition characterized by a pH of about 3.0 to about 4.5 and being free of particulate removable by filtering through a medium with pores no greater than about 50 microns in diameter.
 20. A process comprising: a. contacting a clean magnesium surface with a liquid aqueous composition consisting essentially of a water solution of about 9.4 to about 19.5 grams per liter NH4 , about 50 to about 103 grams per liter PO4 , about 1.0 to about 2.8 grams per liter Ca , and a total of about 1.9 to about 4.8 grams per liter of ions selected from the group consisting of Cl , NO3 , and SO4 , said composition being characterized by a pH of about 3.0 to about 4.5 at a temperature of up to about 120*F.; b. rinsing the contacted surface in liquid water at a temperature of up to about 130*F.; c. drying the rinsed surface; and d. applying a photoresist material to the dried surface.
 21. An aqueous magnesium surface treating compositon comprising: about 60 to about 125 grams per liter of monobasic ammonium phosphate; sufficient calcium salt of a strong mineral acid to produce a Ca concentration of about 1.0 to about 2.8 grams per liter; and sufficient pH modifier elected as required from the group consisting of phosphoric acid and ammonium hydroxide to produce a pH of about 3.0 to about 4.5.
 22. The aqueous composition of claim 21 including sufficient pH modifier to produce a pH of about 3.4 to about 3.7.
 23. The aqueous composition of claim 21 wherein the calcium salt is calcium chloride.
 24. The aqueous composition of claim 21 wherein the calcium salt is calcium nitrate.
 25. The aqueous composition of claim 21 wherein the calcium salt is calcium sulfate.
 26. The aqueous composition of claim 21 comprising about 80 to about 105 grams per liter monobasic ammonium phosphate; and sufficient calcium salt to produce a Ca concentration of about 1.8 to about 2.4 grams per liter.
 27. The aqueous solution of claim 26 including sufficient pH modifier to produce a pH of about 3.4 to about 3.7.
 28. A process comprising: a. contacting a clean magnesium surface with a liquid aqueous composition of claim 27 at a temperature of up to about 120*F., and b. rinsing the contacted surface in liquid water at a temperature of up to about 130*F.
 29. The process of claim 28 including the additional step of removing precipitate from the composition prior to step (a).
 30. The process of claim 28 including as step (c) drying the rinsed surface.
 31. The process of claim 30 including as step (d) applying a photoresist material to the dried surface.
 32. The process of claim 30 including as step (d) applying paint to the dried surface.
 33. The process of claim 30 wherein contacting is carried out with the aqueous composition after filtering the composition through a medium with pores no greater than about 50 microns in diameter.
 34. The process of claim 33 wherein the pores are no greater than 25 microns in diameter.
 35. The process of claim 30 wherein contacting is carried out at a temperature of about 70*F. to about 90*F.
 36. The process of claim 32 wherein the magnesium surface is contacted with the aqueous composition for a time of up to about one minute.
 37. A process comprising mixing together: a. water; b. about 60 to about 125 grams per liter of final composition of monobasic ammonium phosphate; c. sufficient calcium salt of a strong mineral acid to produce a Ca concentration of about 1.0 to about 2.8 grams per liter of final composition; and d. sufficient pH modifier to adjust the pH of the final composition to about 3.0 to about 4.5 wherein the pH modifier is selected as required from the group consisting of phosphoric acid and ammonium hydroxide.
 38. The process of claim 37 wherein step (b) comprises mixing about 80 to about 105 grams per liter of final composition of monobasic ammonium phosphate; and step (c) comprises mixing sufficient calcium salt to produce a Ca of about 1.8 to about 2.4 grams per liter of final composition.
 39. The process of claim 37 wherein step (c) comprises mixing an aqueous solution of the calcium salt.
 40. The process of claim 37 wherein step (d) comprises adding sufficient pH modifier to adjust the pH to about 3.4 to about 3.7.
 41. The process of claim 37 wherein the calcium salt is calcium chloride.
 42. The process of claim 37 wherein the calcium salt is calcium nitrate.
 43. The process of claim 37 wherein the calcium salt is calcium sulfate.
 44. The process of claim 37 including removing precipitate from the final composition.
 45. The process of claim 44 wherein removing calcium phosphate precipitate is carried out by filtering through a medium with pores no greater than about 50 microns in diameter.
 46. The process of claim 37 comprising sequentially mixing together in water diluted phosphoric acid the constituents of steps (b), (c), and (d).
 47. The process of claim 46 including removing precipitate from the final composition.
 48. A process comprising: a. mixing phosphoric acid with water to form a composition; b. mixing about 60 to about 125 grams per liter of final composition of monobasic ammonium phosphate into the composition of step (a); c. mixing into the composition of step (b) sufficient calcium salt of a strong mineral acid in aqueous solution to produce a final Ca concentration of about 1.8 to about 2.4 grams per liter of final composition; d. adding sufficient pH modifier to the composition of step (c) to adjust the pH to about 3.4 to about 3.7 wherein the pH modifier is selected from the group consisting of phosphoric acid and ammonium hydroxide; e. adding sufficient water to the composition of steps (a), (b), (c), and (d), to attain the desired volume; f. filtering the composition of step (d) through a medium with pores no greater than about 50 microns in diameter; g. contacting a clean magnesium surface with the composition of step (f) at a temperature of about 70*F. to about 90*F. for up to about 1 minute; h. rinsing the contacted surface in liquid water at a temperature of up to about 130*F.; i. drying the rinsed surface; and j. applying a photoresist material to the dried surface to form photoengraving sheet.
 49. The process of claim 48 wherein the calcium salt is calcium chloride.
 50. The process of claim 48 wherein the calcium salt is calcium nitrate.
 51. The process of claim 48 wherein the calcium salt is calcium sulfate.
 52. The process of claim 48 wherein the magnesium surface is of an alloy having a designation of PE.
 53. The process of claim 48 wherein a polyvinyl cinnamate type photoresist is applied to the dried surface.
 54. The process of claim 48 wherein the magnesium surface is contacted with the aqueous composition for a time of from about 15 to about 45 seconds.
 55. The process of claim 48 wherein the pores are no greater than 25 microns in diameter.
 56. The process of claim 48 wherein the magnesium surface in step (g) is immersed in the composition oF step (f).
 57. The process of claim 48 wherein the magnesium surface in step (g) is sprayed with the composition of step (f).
 58. The process of claim 48 wherein the treated and dried surface having photoresist applied thereon has shelf-life of at least about 6 months.
 59. The process of claim 48 wherein a phosphate containing layer is formed on the magnesium surface contacted with the composition, the photoresist containing layer promoting effective adhesion of a photoresist material to the magnesium surface. 